Software Engineering Prof. Dr. Bertrand Meyer March 2007 – June 2007 Chair of Software Engineering Software development: “Process” vs “agile” with material

Software EngineeringProf. Dr. Bertrand Meyer

March 2007 – June 2007

Chair of Software Engineering

Software development:“Process” vs “agile”

with material by Marco Piccioni

Software Engineering, lecture 8: Process vs Agile 2

Three cultures of software development

Three cultures:

Process

Agile

Object

The first two are usually seen as exclusive, but all have major contributions to make


Process-oriented

(Sometimes called formal )Examples:

Waterfall model (from 1970 on) Military standards CMM, then CMMI ISO 9000 series of standards Rational Unified Process (RUP) Cluster model

Overall idea: to enforce a strong engineering discipline on the software development process Controllability, manageability Traceability Reproducibility


Agile

Extreme Programming (XP)Lean ProgrammingTest-Driven Development (TDD)Scrum


This lecture (today and tomorrow)

1. The case for agile methods 2. Process-oriented methods 3. Towards a combination


- 1 -

The case foragile methods

(or: the Cubicle Strikes Back)


“The agile manifesto”

We are uncovering better ways of developing software by doing it and helping others do it.

Through this work we have come to value:

Individuals and interactions over processes and tools

Working software over comprehensive documentation

Customer collaboration over contract negotiation Responding to change over following a plan

That is, while there is value in the items on the right, we value the items on the left more.

agilemanifesto.org


Scheme 1: predictable manufacturing

Assembly-line production is possible: Define specifications and constructions steps Build some instances and perform

measurements On the basis of that experience, estimate &

schedule future production


Scheme 2: new model development

Each model specific, evolving process: Requirements change between races

Static reasons (specific tracks) Dynamic reasons (weather, competitors)

High level of competition Continuous experimenting

Prototypes rather than products


Assembly-line vs prototype

Assembly-line manufacturing

Prototype-style manufacturing

Specify, then build Hard to freeze specifications

Reliable effort and cost estimates are possible, early on

Estimates only become possible late, as empirical data emerge

Can identify schedule and order all activities

Activities emerge as part of the process

Stable environment Many parameters change; need creative adaptation to change

C. Larman Agile & Iterative Development A Manager guide Addison Wesley 2003


What about software?

In the agile view, most software development is not a predictable, mass-manufacturing problem, but falls under the new product development model


Agile methods: basic concepts

Principles:Iterative developmentCustomer involvementSupport for changePrimacy of codeSelf-organizing teamsTechnical excellenceSearch for simplicity

Practices: Evolutionary

requirements Customer on site User stories Pair programming Design & code standards Test-driven development Continuous refactoring Continuous integration Timeboxing Risk-driven development Daily tracking Servant-style manager

Shunned: “big upfront requirements”; plans; binding documents; diagrams (e.g. UML); non-deliverable products


Another view: lean programming

Eliminate waste Minimize inventory Maximize flow Pull from demand Empower workers Meet customer requirements Do it right the first time Abolish local optimization Partner with suppliers Create a culture of continuous

improvement

Mary Poppendieck*

*See www.poppendieck.com

“Documentation that is not part of the final

program”

Iterative development

Decide as late as possible

Build in tests;build in changeFret about

value, not scope


Manager’s role in agile development

The manager does not: Create a work

breakdown structure, schedule or estimates

Tell people what to do (usually)

Define and assign detailed team roles

The manager does provide: Coaching Service and leadership Resources Vision Removal of impediments Promotion of agile

principles



Each iteration is a self-contained mini-project

Iteration goal: a release, that is a stable, integrated and tested partially complete system

All software across all teams is integrated into a release each iteration

Most iteration releases are internal

During each iteration, there should be no changes from external stakeholders



Not a new idea (see Microsoft’s Daily Build, cluster model)

Avoid “big bang” effect of earlier approaches

Short iteration cycles


The waterfall modelFeasibility

study

Requirements

Specification

Globaldesign

Detaileddesign

Implemen-tation

Distribution

V & V


Waterfall risk profile

Requirements Design Implementation Integration, V&V…

Time

Po

ten

tial

imp

act

of r

isk

bei

ng

tac

kled

C. Larman Agile & Iterative Development A Manager guide Addison Wesley 2003 p. 58


Risk-driven vs. client-driven planning

What would you choose to implement first?

The riskiest, most difficult tasks…or

What the client perceives as his highest business value?


Timeboxed iterative development

Set iteration end date, no change permitted

If requests cannot be met within timebox:

Place lower priority requests back on wish list Never move a deadline Never ask developers to work more to meet a deadline

Iterations may typically last from 1 to 6 weeks


Parkinson’s law*

Work expands so as to fill the time available for its completion

*C. Northcote Parkinson: Parkinson's Law, or The Pursuit of Progress, 1957


Arguments for timeboxing

For developers: More focus (to limit Parkinson’s law) Forced to tackle small levels of complexity

For managers: Early forcing difficult decisions and trade-offs Better skill assessment of people involved and

better balance and optimization providedFor stakeholders:

They see the actual progress of the application every iteration end


Arguments against upfront requirements

Details are too complex for people to grasp Stakeholders are not sure what they want They have difficulty stating it Many details will only be revealed during

development As they see the product develop, stakeholders will

change their minds External forces cause changes and extensions

(e.g. competition)


Requirements uncertainty

Jones C. 1997 Applied Software Measurement MCGraw Hill

0

5

10

15

20

25

30

35

Requirements change

10 100 1000 10000

Project size in FP


Actual use of requested features

Never: 45%Seldom: 19%Occasionally: 16%Often: 13%Always: 7%

J. Johnson, XP2002


Requirements in practice, the agile view

Realistic approach, based on 200+ SW projects:

Requirements always change Developers get complete specifications only 5%

of the times On average, design starts with 58%

requirements specified in detail

From: D. Reinertsen, S. Thomke: Agile Product Development: Managing Development Flexibility in Uncertain Environments, in California Management Review, Vol. 41, No. 1, Fall 1998, pp. 8-30.


Evolutionary requirements analysis

Do we need to know all the functional requirements to start building a good core architecture?

Agile answer: the architect needs most nonfunctional or quality requirements (e.g. load, internationalization, response time) and a subset of functional requirements


User stories


Test-Driven Development: basic cycle

1. Add a test2. Run all tests and check the new one fails3. Implement code to satisfy functionality4. Check that new test succeeds5. Run all tests again to avoid regression6. Refactor code

After Kent Beck*

*Test Driven Development: By Example, Addison-Wesley


TDD: a first assessment

For: Central role to tests Need to ensure that all

tests pass Continuous execution

But: Tests are not specs Risk that program pass

tests and nothing else

Stay tuned…


Scrum practices

Self-directed and self-organizing teams of max 7 people

No external addition of work to an iteration, once chosen

Daily team measurement via a stand-up meeting called “scrum meeting”

30 calendar-day iterations Demo to stakeholders after each iteration


Scrum lifecycle

Planning

Staging

Development

Release


Scrum lifecycle: planning

Purpose: Establish the vision Set expectation Secure funding

Activities: Write vision Write budget Write initial product backlog Estimate items Exploratory design and prototypes


Scrum lifecycle: staging

Purpose: Identify more requirements and prioritize

enough for first iteration

Activities: Planning Exploratory design and prototypes


Sample product backlogRequirement N. Category Status Pri Est.(hrs)

log credit payments to AR

17 feature underway

5 2

process sale cash scenario

97 use case underway

5 60

slow credit payment approval

12 issue not started

4 10

sales commission calculation

43 defect complete

4 2

lay-away plan payments 88 enhance not started

3 20

PDA sale capture 53 technology

not started

1 100

process sale c.c. scenario 71 use case underway

5 30



Scrum lifecycle: development & release


XP practices: about people

Team typically works in an open space.

Stakeholders are mostly available

Every developer chooses his tasks (iteration planning game)

Pair programming

No overtime (sustainable pace)

Documentation: reduced to bare minimum


XP lifecycle

Exploration

Planning

Iterations to first release

Productizing

Maintenance


XP lifecycle: exploration

Purpose: Enough well-estimated user stories for first

release Feasibility ensured

Activities: Prototypes Exploratory proof of technology programming Story card writing and estimating


XP lifecycle: planning

Purpose: Agree on date and stories of first release

Activities: Release planning game Story card writing and estimating


XP lifecycle: iterations to first release

Purpose: Implement a tested system ready for release

Activities: Testing and programming Iteration planning game Task writing and estimating


XP lifecycle: productizing

Purpose: Operational deployment

Activities: Documentation Training Marketing


XP lifecycle: maintenance

Purpose: Enhance, fix Build major releases

Activities: May include this phases again, for

incremental releases


What about tools?

Try to keep things as simple as possible

Only if they really help productivity and information sharing

Ideal situation: one relatively simple tool that seamlessly embraces all software lifecycle

Examples: No tool (white board + camera or video), Eiffelstudio, IBM Jazz project


Agile methods links

www.agilealliance.comwww.cetus-links.orgwww.xprogramming.comwww.gilb.comwww.craiglarman.comwww.controlchaos.comwww.pols.co.uk/agile-zone/papers.htmlwww.eiffelroom.com

http://www.agilealliance.com/

http://www.cetus-links.org/

http://www.xprogramming.com/

http://www.gilb.com/

http://www.craiglarman.com/

http://www.controlchaos.com/

http://www.pols.co.uk/agile-zone/papers.html

http://www.eiffelroom.com/


Not everyone is gaga about XP


Criticisms of XP

Hype not backed by evidence of success Loony ideas

(e.g. pair programming) “What’s good is not new, what’s new is not good” Rejection of proven software engineering

techniques Lack of design

(disdained in favor of refactoring) Lack of documentation

(disdain of “big upfront requirements”) Unfairly favors developer over customer Complicates contract negotiations


Pair programming criticism

“Pair programming is necessary in XP because it compensates for a couple of practices that XP shuns: up-front-design and permanent documentation.

It makes up for the fact that the programmers are (courageously) making up the design as they code”.

(Stephens & Rosenberg)*

*Slightly abridged

(Ron Jeffries: “I think maybe concentration is the enemy. Seriously. If you’re working on something that is so complex that you actually need to concentrate, there’s too much chance that it’s too hard”)


At first (Stephens & Rosenberg)


“None of this actually matters” (Stephens & Rosenberg)


The cycle (Stephens & Rosenberg)


Contract-Driven Development

CDD = TDD — WTC*

Use contracts as specifications and test oracles

*Writing Test Cases

Andreas Leitnerwith Arno Fiva

(ETH)

53

Specified but unimplemented routine

54

Running the system and entering input

54

(erroneou

s)

55

The error is flagged at run time as a contract violation

55

56

This has become a test case

56

57

Another execution, another error

57

58

This has become a second test case

58

59

Editing the class

59

60

Correcting an error

60

61

Recompiling

61

62

Test cases are run again silently in the background

62

6363

One bug corrected, the other not

64

Attempting a fix

64

65

Still doesn’t work

65

66

We fix this (or think so)

66

67

The guardian angel is, however, watching

67

68

They fixed the bugs, had many children and lived happy ever after

68


- 2 -

Process-based approaches:

RUP


Rational Unified Process (RUP)

Process model designed by Rational (now IBM) on basis of Spiral model (Boehm) Objectory (Jacobson)


RUP practices

Risk-driven requirements handling using use cases

Visual modelling

Develop in short timeboxed iterations

Focus on component architectures

Continuous measurement of quality factors

Up to 50 artifacts, all optional


RUP: sample disciplines and artifacts

Discipline Artifact (Workproduct)Requirements Vision

Use-Case Model

Design Design model

Software Architecture Document

Project Management Iteration Plan

Risk List



RUP lifecycle

Inception

Elaboration

Construction

Transition


RUP phases


- 3 -

The good, the bad and the ugly


Retain from XP

Principles: Iterative development Customer involvement Support for change Primacy of code Self-organizing teams Technical excellence Search for simplicity

Practices: Evolutionary

requirements Customer on site User stories Pair programming Design & code standards Test-driven development Continuous testing Continuous refactoring Continuous integration Timeboxing (where

appropriate) Risk-driven development Daily tracking Servant-style manager


Discard from XP

Pair programming as an imposed practiceRefusal to guarantee both functionality and delivery

dateTests as a substitute for specifications


Retain against XP

Key software engineering practices: Extensive requirements process Documentation Upfront design Specifications as subsuming tests Role of manager Commitment to both functionality and date Design for generality


Retain from process-based approaches

Engineering principlesDocumentationIdentification of tasksIdentification of task dependencies


Reject from process-based approaches

Strict separation between analysis, design, implementation

Ignorance of the central role of change in software

Use cases as the principal source of requirements

Tendency to “Big Bang” effect


The contribution of object technology

Focus on abstractions

Reuse (consumer and producer)

Seamless development

Reversibility

Single Model principle: The software is the

model The model is the

software The software includes

everything relevant to the project

Tools automatically extract views

See B. Meyer, PracticeTo Perfect:The Quality First Model, IEEE Computer, May 1997, pages 102-106, also at se.ethz.ch/~meyer/publications/computer/quality_first.pdf

(“Primacy” of code, but in a more far-reaching sense than in plain XP)

Contracts as a guide to analysis, design, implementation, maintenance, management

Continuous testing based on contracts

http://se.ethz.ch/~meyer/publications/computer/quality_first.pdf



8282

Seamless development with Eiffel & contracts

Single notation, tools, concepts, principles

Continuous, incremental development

Keep model, implementation, documentation consistent

Reversibility

Example classes:PLANE, ACCOUNT, TRANSACTION…

STATE, COMMAND…

HASH_TABLE…

TEST_DRIVER…

TABLE…

Analysis

Design

Implemen-

tation

V&V

Generali-zation

83

Software Engineering

The cluster model

Cluster 1Cluster 2A

D

I

V&V

G

AD

I

V&V

G

AD

I

V&V

G

AD

I

V&V

G

84


The cluster model

I

V

D

S

GI

V

D

S

GI

V

D

S

G

Cluster 1Cluster 2

I

V

D

S

G

Cluster n

I

V

D

S

G

I

V

D

S

G

85


Cluster model: focus & practices

Clusters (set of related classes) Start with foundational clusters Mini lifecycles, each covering a cluster Seamlessness Reversibility Design by contract Current showable demo at every stage

86


Mini-lifecycle tasks

Specification Design / Implementation Verification & Validation Generalization

87


Mini-lifecycle tasks: specification

Identification of the data abstractions (classes) of the cluster

Identification of constraints (class invariants)

88


Mini-lifecycle tasks: design & implementation

Definition of the class architecture Interface features Contracts

Definition of the relationships between classes Client Inheritance

Finalization of classes

89


Mini-lifecycle tasks: verification & validation

Static examination

(Possibly) automated unit testing

90


Mini-lifecycle tasks: generalization

Goal: turn classes in potentially reusable software components via:

Abstracting

Factoring

Documenting

91


Generalization

Prepare for reuse. For example: Remove built-in limits Remove dependencies on

specifics of project Improve documentation,

contracts... Abstract Extract commonalities and

revamp inheritance hierarchy

Few companies have the guts to provide the budget for this

B

A*

Y

X

Z

A D I V G

92


Software engineering principles

Quality pays

Architecture

Extendibility

Reusability

Reliability

Documents

Software Engineering Prof. Dr. Bertrand Meyer March 2007 – June 2007 Chair of Software Engineering Software development: “Process” vs “agile” with material